Abstracts

Rationale: Patients with pharmacoresistant epilepsy benefit from functional hemispherectomy (HE) in 60-80% of all cases. However, 20-40% of postsurgical patients continued to have seizures. In some patients poor postsurgical seizure outcome might be explained by contralateral seizure onsets, but in a subgroup seizures seem to continue to be generated by the presumingly disconnected hemisphere. In this group disconnection of the remaining interhemispheric connection has been described as curative. This study aimed to show the correlation between the presence of postsurgical interhemispheric connections (corpus callosum (CC), anterior/posterior commissure (AC/PC)) detected by MRI and the occurrence of postsurgical seizures. Methods: All patients who underwent functional HE using a perisylvian approach at Freiburg Epilepsy Center between 2011-2018 and received a postsurgical MRI were included. Seizure outcome was evaluated at least 12-month postoperatively. MRI scans were visually analyzed by two independent reviewers using Nora, an institutional software for medical image analysis (http://www.nora-imaging.com). Particular focus was put on the splenium and the genu of corpus callosum as well as the anterior and posterior commissure. Results: Fifty-six patients could be included (50 children/6 adults). Follow-up and postsurgical MRI scans were present in 49 cases. A total of 35 (71.42) patients were seizure- free with a median follow up 24 month(Figure 1). In the majority of patients CC was disconnected and AC and PC remained as expected in this surgical approach. In 3 of 35 (8.58%) of seizure-free patients, MRI showed a remaining connection in CC, in 100% a remaining PC and 97.14% AC (Figure 2). 14 patients continued to have seizures, 7 of whom were hypothesized to derive from the operated hemisphere. Three (42.86%) of these 7 patients had a remaining interhemispheric connection via CC. The other 4 (57.14%) patients had a disconnected CC but remaining PC and AC. In two of the seven cases, the patient became seizure-free after a second intervention with thermoablation of remaining interhemispheric connections. Conclusions: In this study, we could show that patients who continue to seize with similar semiology and EEG patterns after surgery more often showed remaining connections via the corpus callosum than seizure free patients. Some patients might profit from a complete disconnection of all structures. A closer inspection of postoperative MRIs assessing the especially CC but also AC and PC might therefore give important clinical information in this patient group. Stereotactic ablation of remaining connections might be a treatment option for some patients. Moreover this study raises the question whether surgical approaches which allow an intraoperative visualization of all connecting structures might be preferable when performing hemispherotomies. Funding: No funding